In typical PTCA procedures, a guiding catheter is percutaneously introduced into the cardiovascular system of a patient through a vessel and advanced through therein until the distal end thereof is at a desired location in the vasculature. A guidewire and a dilatation catheter having a balloon on the distal end thereof are introduced through the guiding catheter with the guidewire sliding through the dilatation catheter. The guidewire is first advanced out of the guiding catheter into the patient's coronary vasculature and the dilatation catheter is advanced over the previously advanced guidewire until the dilatation balloon is properly positioned across the lesion. Once in position across the lesion, the flexible, expandable, preformed balloon is inflated to a predetermined size with a liquid or gas at relatively high pressures, such as greater than about four atmospheres, to radially compress the artirosclerotic plaque of the lesion against the inside of the artery wall and thereby dilate the lumen of the artery. The balloon is then deflated to a small profile so that the dilatation catheter may be withdrawn from the patients vasculature and blood flow resumed through the dilated artery.
In angioplasty procedures of the kind described above, there may be injury to or restenosis of the artery, which either necessitates another angioplasty procedure, a surgical by-pass operation, or some method of repairing or strengthening the area. To strengthen the area and help prevent restenosis, a physician can implant an intravascular prosthesis for maintaining vascular patency, commonly called a stent, inside the artery at the lesion. The stent is expanded to a larger diameter for placement in the vasculature, often by the balloon portion of the catheter. Stents delivered to a restricted coronary artery, expanded to a larger diameter by a balloon catheter, and left in place in the artery at the site of a dilated lesion are shown in U.S. Pat. No. 4,740,207 to Kreamer and U.S. Pat. No. 5,007,926 to Derbyshire, the content of which is incorporated herein by reference. Palmaz et al., 156 Radiology 73 (1985) and U.S. Pat. No. 4,733,665 describe introduction of a stent over a balloon catheter (incorporated herein by reference).
To assist in accurate placement of the catheter and stent underneath the lesion site it is useful to visually monitor the catheter as it advances through a vessel. Fluoroscopes or other similar X-ray emitting devices are used to view the catheter within the body as it is advanced. However, in order for the catheter to be visible when exposed to X-rays, the catheter or a portion of the catheter, must be radiopaque to X-rays. In previous catheter designs, radiopaque marker bands or catheter tips are often attached to the catheter for this purpose.
An initial example of a catheter which utilizes an external metal radiopaque marker band is U.S. Pat. No. 5,759,174 to Fischell et al., the entire contents of which are hereby incorporated by reference, which has a single external metal marker band which is intended to identify the central portion of a stenosis once the delivery catheter is removed. Marker bands such as those disclosed by Fischell et al. are normally mounted externally on the delivery catheter and undesirably increase the profile of the catheter as well as its cost. Furthermore, marker bands are constructed from expensive and heavy radiopaque metals such as gold, platinum and tantalum or alloys of these dense materials. Marker bands constructed from these metals are also costly to manufacture.
Despite these shortcomings, marker bands are preferable over radiopaque tips alone, since a radiopaque catheter tip only provides for the end of the catheter to be visible as opposed to a desired area along the catheter shaft. For example, U.S. Pat. No. 5,429,597 to Demello et al., the entire contents of which are hereby incorporated by reference, discloses a balloon catheter having a radiopaque distal tip composed of a polymer mixed with a radiopaque powder such as tungsten. Such a tip is visible under X-ray observation. In addition Demello et al., discloses a preferred embodiment which uses of two metal radiopaque marker bands located along a core wire to better track the expandable region of a balloon.
U.S. Pat. No. 4,866,132 to Obligin et al.; U.S. Pat. No. 5,256,334 to Smid et al.; and U.S. Pat. No. 5,024,232 to Smid et al., the entire contents of each being hereby incorporated by reference, respectively disclose various methods of making radiopaque polymer complexes. The references also suggest using radiopaque polymer complexes with existing implantable devices which are presently used with radiolucent plastics. These references do not however, disclose the present catheter which is constructed with radiopaque polymer hubs as disclosed below, and where the hubs provide the dual function of stent crimping and marker bands.